In a single sheet plasma processing apparatus, it is typical that, within an evacuatable processing chamber, a target substrate (e.g., a semiconductor wafer) is mounted on a mounting table called a susceptor or other names and is subjected to plasma processing such as dry etching, oxidizing, depositing or the like.
In general, the susceptor serving as a radio frequency (RF) electrode is made of a material with superior conductivity and workability, e.g., aluminum, and is attached within the processing chamber in a non-grounded state, namely in an electrically floating state. During the plasma processing process, a RF power supply arranged outside the processing chamber applies a RF power of a specified frequency to the susceptor via a matching unit.
In a mechanical aspect, lift pins for loading an unprocessed substrate to the susceptor and unloading a processed substrate from the susceptor are movable upwards and downwards through the susceptor.
In order to control the temperature of the substrate under plasma processing, a coolant flow path for cooling and a heating element for heating are provided within the susceptor. For efficient thermal transfer from the susceptor to the substrate in this case, a heat transfer gas (typically, a helium gas) is supplied at a predetermined pressure to the rear surface of the substrate through a gas flow path formed in the susceptor.
The plasma processing apparatus using the susceptor as set forth above includes an electrostatic chuck unitarily formed with the major surface, i.e., the substrate mounting surface, of the susceptor for holding the substrate on the susceptor (see, e.g., Japanese Patent Laid-open Application No. 2005-123578 and corresponding U.S. Patent Application Publication No. 2005-95732A). The electrostatic chuck of this kind has a structure in which a thin conductor (electrode) is encapsulated within a dielectric film. A high DC voltage of, e.g., 2 to 3 kV, is applied to the conductor to generate an electrostatic force in the substrate mounted on the susceptor, thereby attracting and holding the substrate with a Coulomb force.
With the plasma processing apparatus in which the susceptor serves as a RF electrode as noted above, there is a problem in that, if the high DC voltage is applied to the conductor of the electrostatic chuck prior to starting the plasma processing process, the gas (especially, the heat transfer gas) undergoes abnormal electric discharge between the substrate and the susceptor immediately after the voltage application, which makes the substrate susceptible to damage (at least with random probability).
More specifically, the electrostatic chuck is provided with through-holes through which to pass the lift pins and the heat transfer gas. These through-holes form gas spaces between the substrate and the susceptor. If the high DC voltage is applied to the conductor of the electrostatic chuck, the electric potential of the substrate and the susceptor is instantly increased by electrostatic induction up to substantially the same electric potential as the high DC voltage. Just after then, the electric charges of static electricity flow from the substrate to a chamber sidewall or an upper electrode, which is kept at a ground potential, through the processing space defined within the processing chamber. Thus, the electric potential of the substrate is decreased to the ground potential. On the other hand, the electric charges of static electricity continue to stay in the susceptor so that the electric potential of the susceptor is kept at the same level as that of the high DC voltage. Therefore, almost the same voltage as the high DC voltage is applied to the gas present in the through-holes of the electrostatic chuck between the substrate and the susceptor. Abnormal electric discharge occurs if the discharge-starting conditions under Paschen's Law are satisfied.